Lubricants, such as those used in a variety of machinery, are susceptible to oxidative deterioration during storage, transportation, and usage, particularly when such lubricants are exposed to high temperatures and iron catalytic environments, which greatly promote their oxidation. This oxidation, if not controlled, contributes to the formation of corrosive acidic products, sludge, varnishes, resins, and other oil-insoluble products and may lead to a loss of physical and tribological properties of the lubricants. Oxidation of aviation lubricants, such as synthetic polyol esters, is particularly undesirable, given the potential consequences of in-flight engine failure. It is therefore a common practice to include antioxidant additives in lubricants to prevent, at least to some extent, oxidation, so as to extend the useful life of the lubricants.
Alkylated diphenylamines are widely known in the art as antioxidants. Commercial applications include lubricants, rubber, plastics, polyurethanes, hydraulic fluids, greases and fuels.
The use of 1,4-benzenediamines is also known, as exemplified in U.S. Pat. Nos. 2,718,501, 2,883,362, 3,211,793, 3,304,285, and 5,711,767, U.S. Publication Nos. 2006/0128574, 2006/0189824, and 2007/0006855, GB1296592, and GB0835826 and JP59020392, the disclosures of which US patents and applications are incorporated herein by reference. 1,4-benzenediamines have more commonly been employed as motor fuel stabilizers and antiozonants and antioxidants for rubber.
U.S. Pat. No. 2,451,642 discloses meta-phenylenediamine, N1,N3-dimethyl-meta-phenylenediamine, and lauryl-meta-phenylenediamine as useful antioxidants for lubricating oil compositions in environments where iron-catalyzed oxidation reaction can take place. N,N′-dimethyl-ortho-phenylenediamine, N,N′-dicyclohexyl-para-phenylenediamine, and various di- and tetra-n-alkyl-para-phenylenediamines are similarly disclosed.
U.S. Pat. No. 2,718,501 discloses a stabilizer system consisting of an aromatic amine with at least two aromatic rings, including N,N′-diphenyl-para-phenylenediamine, and an organic aliphatic sulfur compound, which is said to be suitable for stabilizing mineral hydrocarbon lubricating oils, synthetic hydrocarbon oils, and polyalkylene glycol oils.
U.S. Pat. No. 2,857,424 discloses the preparation of oxalic acid salts of fuel stabilizing N,N′-dialkyl-para-phenylenediamines as a way of rendering the additives less toxic.
U.S. Pat. No. 3,402,201 discloses N,N′-dicyclooctyl-p-phenylenediamine as a stabilizer for organic materials, particularly rubber, and exemplifies its use as a gasoline inhibitor. The similar use of N,N′-dicyclooctyl-o- and m-phenylenediamines is contemplated.
U.S. Pat. Nos. 5,207,939 and 5,312,461 disclose certain Mannich base reaction products of mono- or dialkyl-phenylenediamines, an aldehyde or ketone, and a hindered phenol, which can be used in an antioxidant amount in lubricating oils, greases, and fuel compositions.
U.S. Publication No. 2006/0128574 discloses the use of physical mixtures of secondary diarylamines in combination with N,N′-dialkyl-para-phenylenediamines, and optionally hindered phenolics, as stabilizers for lubricants and fuels, but is silent regarding improvements in performance that may be achieved by reaction products thereof.
U.S. Publication No. 2006/0189824 discloses various N-alkyl-N-(dialkylhydroxyphenyl)alkyl-N′-phenyl-para-phenylene diamines, methods for their preparation by Mannich reactions of dialkylphenols with N-phenyl-para-phenylenediamines, and their use as antioxidants.
U.S. Publication No. 2007/0006855 discloses the use of alkylated para-phenylenediamines as soot dispersants in passenger car and heavy-duty diesel engines equipped with exhaust gas recirculation systems. An extremely broad scope of polyalkylated para-phenylenediamines is disclosed for this specific application alone.
Japan Patent No. 59-020,392 discloses a lubricant composition comprising N, N′-di-sec-butyl-para-phenylenediamine for pressure forming of oil tanks. The lubricant composition also contains hindered phenolic antioxidant.
Oberster, A. E. et al., 45 CAN. J. CHEM. 195-201 (1967), prepared 39 novel phenylenediamines as part of a program to find antiozonants for rubber that are not sensitizers or dermatotoxic. In some compounds the N′-phenylenediamine nitrogen was variously fused into a pyrrolidine, piperidine, hexamethyleneimine (homopiperidine), morpholine, or 2,6-dimethylmorpholine ring.
Makogon, A. N. et al., 12 KHEMICHESKAYA PROMYSHLENNOST, SERIYA: METODY ANALIZA I KONTROLYA KACHESTVA PRODUKTSII V KHIMICHESKOI PROMYSHLENNOSTI 18-21 (1980), describe the characterization of N, N′-dialkyl-para-phenylenediamines reaction products obtained by the catalytic alkylation of 4-aminodiphenylamine with C7-C9 alcohols.
While phenylenediamines are known to act effectively as antioxidants, the presence of these compounds in amounts conventionally used to provide antioxidancy displayed aggressiveness toward fluoroelastomeric engine seal materials. These adverse effects are particularly apparent with phenylenediamine compounds having higher nitrogen contents (compounds having relatively small hydrocarbyl substituents).
U.S. Pat. Nos. 3,509,214 and 3,573,206 describe the use of inorganic oxidants, such as potassium permanganate, lead dioxide, manganese dioxide, and hydrogen peroxide to prepare an oligomeric mixture between a phenyl naphthylamine and an alkylated diphenylamine. However potassium permanganate or manganese dioxide form very fine precipitates that readily clog filter apparatus. Lead dioxide is to be avoided for obvious environmental reasons.
U.S. Pat. Nos. 3,901,815 and 4,064,059 disclose compositions of alkylated phenylnaphthyl-amines and alkylated diarylamines as antioxidants for pentaerythritol and trimethylolpropane ester aviation turbine lubricants.
U.S. Pat. No. 4,110,234 describes the stabilization of a poly alpha olefin oil with an antioxidant comprising an alkylated phenyl naphthylamine, a sulfur compound, and a trace amount of a metal, such as copper or nickel. U.S. Pat. No. 4,122,021 describes the stabilization of any of a poly alpha olefin, a highly saturated mineral oil, or and ester oil with an antioxidant comprising an alkylated phenyl naphthylamine and a sulfoxide. U.S. Pat. No. 4,770,802 claims phenyl napthylamines that are substituted with a branched chain of 12 to 15 carbons.
U.S. Pat. No. 5,160,647 teaches the Mannich dimer product 4,4′-methylenebis[N-(4-tert-octylphenyl)-1-naphthylamine] as an antioxidant for aircraft turbine lubricants.
U.S. Pat. No. 6,426,324 describes the use of an organic peroxide radical source to prepare an oligomeric mixture between two diarylamines, e.g., a phenyl naphthylamine and an alkylated diphenylamine. The mole ratio of diphenylamine to phenyl naphthylamine is between 1:1 and 10:1. The patent does not contemplate the use of an organic peroxide radical source to prepare an oligomeric mixture between a phenyl naphthylamine and a substituted phenylenediamine.
U.S. Pat. No. 7,307,049 discloses reaction products of alkylated phenyl naphthylamines and formaldehyde as antioxidants for synthetic polyol ester lubricating oils.
EP 606,863 A3 discloses alkylated phenyl naphthylamines as antioxidants for oxyalkylene glycols and their mono- and dialkyl ethers.
EP 2,055,763 A1 describes the use of an alkylated phenyl naphthylamine in combination with two different alkylated diphenylamines as antioxidants, at least one of which has a number average molecular weight of from 321 to 700. The arylamine antioxidants in question are all well known commercially available materials which do not contain additional arylamine substituents or condensates.
The foregoing US disclosures are incorporated by reference.